#include <stdio.h>

int sum( int m, int n ){
	int res = 0,i;
	for (i=m;i<=n;i++){
		res+=i;
	}
	return res;
}

int practice_5_1()
{    
    int m, n;

    scanf("%d %d", &m, &n);
    printf("sum = %d\n", sum(m, n));

    return 0;
}

